Rubber is an example of a natural
polymer. The chains of molecules in rubber have a natural elasticity: they can
stretch when pulled. When the pulling force is removed, the elastic polymers in
rubber spring back to their original length. A polymer with elastic properties
like this is sometimes called an elastomer. The molecular chains of an
elastomer basically act like springs.

When a
rubber band is stretched out, there are not as many ways the individual
molecules can arrange themselves as they are when the rubber band is not
stretched. They have to be lined up. These
links between the chains are called cross links. If too much force is applied
these cross links will break and the rubber band will snap.When there are more ways to arrange the molecules, the entropy is
higher. When a rubber band is stretched, entropy dictates that the rubber band
will want to contract again. When the temperature is higher, the molecules are
more excited, and want even more to be in a random state. This makes the rubber
band easier to stretch out. At a constant
temperature, a rubber band obeys Hooke's Law: The force, f = - K(X - Xo) where
K is a constant, (X - Xo) is the elongation and the sign in negative because
the force is in the direction opposite to the extension. That is the force, f,
is trying to pull the rubber band back to its equilibrium length, Xo.

We
believe that the elasticity of the rubber band is going to increase as the
temperature increases in our experiment.

Elasticity
of the rubber band is defined as the maximum length the rubber band stretches
from its initial length when weight is placed on it. (Dependent Variable) Temperature
is defined as the temperature of the water that the rubber band is submerged in
(Independent Variable). The type and size of rubber band and time of rubber
band submerged in water will be controlled.

Our first
action was to create a contraption which would allow us to determine the
elasticity of rubber bands, while varying both the temperature of the rubber
bands and the amount of weight placed on them. See picture below. Using nails,
we fastened the three pieces of wood together into a frame with a hole in the
top and two pulleys attached, allowing a wire to travel through the hole in the
top of the contraption, then partway down one side of the frame. To the top of
the contraption, we fastened a metal strip that extended downward from the
middle of the apparatus, next to the wire. At one end of the wire we placed a
50 g hook to hold the weights, and on the other end was a small metal clip,
where we attached a rubber band. The rubber band was anchored to a small metal
hook that was attached to the metal strip. We fastened a ruler to the side of
the frame by the weight, in order to measure how much the rubber band
stretched. After the contraption was built, we decided to create different
water temperatures in order to change the temperature of the rubber band. We
put water in a large class container, then cooled it with ice cubes to get our
first temperature of 0 degrees Celsius. We placed the glass container inside the
wood frame, submerging the rubber band. Then, we measured the amount the rubber
band stretched after adding weight to the 50 g weight hook. We calculated the
elasticity of the rubber band at 100, 200, 300, 400, 500, and 600 g. We
repeated this procedure for temperatures of 20, 40, 60, 80, and 100 degrees
Celsius, using the hot plate to bring the water to warmer temperatures. After
collecting data on each new temperature, we switched rubber bands, to minimize
error.

Our results show that the elasticity of a rubber band clearly increases as
temperature increases. Higher temperatures also amplified the affect more weight
had on the rubber band. We used a different rubber band in an attempt to make
our error less, but the fact that once a rubber band stretches out it doesn’t
spring back completely is still cause for some uncertainty. The highest amount
of stretch at 600 gm and 100 C was 17.90 +/- 0.05 cm. The lower amount of
stretch at 100 gm and 0C was 0.50 +/- 0.05 cm. By
looking at the graphs, it is easy to see that the temperature and the amount of
stretch (depending on weight) make a linear trend line because the two factors
are directly related.

The
hypothesis was supported by our experiment. The heated rubber bands were the
most elastic; stretching to the farthest extends of 17.90 +/- o.o5 cm (100 C). The rubber bands in freezing water were
the opposite, with a stretching length of 9.50 +/- o.o5 cm (0
C).The results were consistent, providing a reliable conclusion to the project.
Thermal expansion caused the rubber bands to react as they did. When the rubber
bands were heated, the particles stretched out, making them more elastic and
able to withstand greater force. When frozen, the particles contracted, adding
strength and increasing resistance to force.

Our
results also showed that the effect temperature had on the elasticity of the
rubber bands was amplified under more weight. At lower temperatures the
difference between light and heavy weights was significantly less than the
difference between the same amounts of weight at higher temperatures.

Some
of the sources of error were the initial elasticity of the rubber bands. After
a rubber band was tested at a certain temperature, it could no longer be used.
Therefore, we had to use different rubber bands every time. To reduce this
error we made sure that all of the rubber bands had the same initial stretch;
however, there is still possible error. Another source of error would be the
temperature of the water and rubber band. It was harder to maintain the same
temperature for a period of time. The temperature could have fluctuated during
our experiment, varying out results.

If
we were to conduct this research again, we would not control the amount of
weight used to stretch the rubber bands. Next time, we could make the model so
that the temperature could be consistent throughout the measurement process.
Also, we would use as much weights as it takes for the rubber band to snap. We
might try to use different types of rubber bands in more temperature values as
well.

3."How rubber band
is made - Background, Raw Materials, The Manufacturing Process of rubber band,
Quality Control, The Future." How Products Are Made. Web. 30 Oct. 2009.
<http://www.madehow.com/Volume-1/Rubber-Band.html>.
This source talks about how rubber bands are formed, and their structure, which
was useful in helping us to predict what would happen to the rubber bands when
stretched.